Method of treating waste water containing ligninsulfonate

ABSTRACT

A method of treating the waste water containing ligninsulfonate, wherein waste water contains sodium salt, calcium salt, potassium salt, etc. of ligninsulfonic acid, comprises the steps of: conducting electrolysis with a ferrous anode plate utilizing said waste water as an electrolyte which has been made to have pH within the range from 5 to 9 prior to the start of electrolysis, while air is being blown therein by a suitable means, whereby said ligninsulfonate is rendered insoluble; and subsequently separating said insoluble substances from the mother liquid by floating them.

1451 Feb. 19, 1974 A METHOD OF TREATING WASTE WATER CONTAININGLIGNINSULFONATE [75] Inventors: Minoru Ichiki; Masahito lshii, both ofTokyo, Japan [73] Assignee: Mitsui Mining & Smelting Co., Ltd.,

Tokyo, Japan 22 Filed: Sept. 6, 1972 21 Appl. No.: 286,713

[30] Foreign Application Priority Data Sept. 9, 1971 Japan 46-69977 [52]U.S. Cl 204/149, 210/44, 204/152, 1 I 204/130 [51] Int. Cl. C02c 5/12[58] Field of Search 204/149, 152, 130, 277; 210/42, 44

[56] References Cited UNITED STATES PATENTS 470,181 3/1892 Collins204/277 X 478,048 6/1892 Collins 204/277 X 2,823,178 2/1958 Ritter.204/131 3,691,041 9/1972 Stralser 204/149 X 3,706,646 12/1972 Gibson,Jr. et al. 204/149 Primary Examiner-John H. Mack Assistant Examiner-A.C. Prescott Attorney, Agent, or Firm-Woodhams, Blanchard &

Flynn 57 ABSTRACT A method of treating the waste water containingligninsulfonate, wherein waste water contains sodium salt, calcium salt,potassium salt, etc. of ligninsulfonic acid, comprises the steps of:conducting electrolysis with a ferrous anode plate utilizing said wastewater as an electrolyte which has been made to have pH within the rangefrom 5 to 9 prior to the start of electrolysis, while air is being blowntherein by a suitable means, whereby said ligninsulfonate is renderedinsoluble; and

subsequently separating said insoluble substances from the mother liquidby floating them.

2 Claims, N0 Drawings METHOD OF TREATING WASTE WATER CONTAININGLIGNINSULFONATE BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention relates to a method of treating waste watercontaining ligninsulfonate.

2. Description of the Prior Art The conventional methods for purifyingwaste water, which is produced by industries employing ligninsulfonateas a raw material and the paper pulp industry, by separatingligninsulfonic acid or ligninsulfonate therefrom, are usually typifiedby the following: A method comprising the steps of first collectingfibers therefrom by screening and neutralizing the waste water withcalcium hydroxide for precipitation; a method wherein the waste water issprayed onto a filtering bed in order to decompose ligninsulfonate; byan activated-sludge method for decomposing ligninsulfonate by bacteriaalso; and an aeration method.

However, the treatment employing chemicals for precipitation requires alarge amount of calcium hydroxide, and also produce a sludge which isdifficult to dehydrate.

Further, a satisfactory efficiency cannot be expected from purificationbased upon the method wherein the waste water is sprayed onto afiltering bed, with regard to a waste water from sulfurous acid pulpcontaining therein free sulfurous acid because this is detrimental tothe bacteria. Also lignins or organic substances of lignin areconsidered, from the microbiological point of view, to be very difficultto decompose.

The aeration method does not demonstrate as much efficiency as thepreceding method does; in other words it is inferior in purifying thewaste water. As to the activated sludge method, it requires a largeamount of water for dilution thereby even after neutralization of freesulfurous acid; accordingly there is some difficulty in application ofthis method.

Furthermore, there are other methods in which oxidation is conducted bymeans of bacteria and the waste water is mixed with the concentratedorganic waste water for methane fermentation. However, a successfulresult could not be expected therefrom because the sulfurous acid,ligninsulfonic acid, etc. restrain the activity of bacteria; accordinglya trial of this method has not been carried out yet.

It is considered that the method of treating waste water wherein saidwaste water is sprayed onto the filtering bed of two steps is the mosteconomical and effective in all the above-mentioned methods, so long asa sufficient area is available.

SUMMARY OF THE INVENTION That is, the present invention relates to amethod of treating waste water containing ligninsulfonate characterizedby the steps of: conducting electrolysis using a ferrous anode plateutilizing said waste water as an electrolyte having pH in the range from5 to 9, while air is blown therein, whereby said ligninsulfonate becomesinsoluble; and subsequently separating said insoluble substances fromthe mother liquid by floating them.

DETAILED DESCRIPTION OF THE INVENTION As is apparent from the foregoingdescription, in the present invention the electrolysis is conductedutilizing the waste water containing ligninsulfonate therein as anelectrolyte.

Thereby it is supposed that, as the electrolysis proceeds,ligninsulfonic acid ion of the said ligninsulfonate (sodium salt,potassium salt, or calcium salt) loses its charge at or in the vicinityof the anode, whereby said ligninsulfonate is rendered insoluble to formfloc.

The matter of primary importance according to the present invention isthat the electrodes, especially the anode, should consist of iron. Theelectrolysis can perform purification of the waste water to some extent,

even when an anode plate made of aluminum is employed. Throughexperiments, however, it has been found out that employment of a ferrousanode plate results in an exceedingly superior efficiency ofpurification in comparison with an anode plate made of other materials.

Well known materials, for instance, such as copper, nickel, iron, etc.are applicable to the cathode plate.

Another matter of importance according to the present invention is tominimize the ferrous ions dissolved in is the electrolyte. This isachieved by blowing sufficient air into the electrolytic cell for'thepurpose of changing divalent ferrous ions, which dissolve from the anodeplate due to the electrolysis, to trivalent ion.

This air-blowing process serves to prevent the cake from adhering to theinside wall of the electrolytic cell, and also causes easy and completeseparation of solid substances from the mother liquid, since thefloating of floc can be easily realized as said floc absorbs enough airtogether with the gas arising from the electrolysis.

Another matter of importance according to the present invention is tokeep the pH of the electrolyte in the range from 5 to 9 by addingthereto acid as required, because the progress of the electrolysis makesthe electrolyte alkaline, and this disturbs oxidation of ferrous lOllS.

Even when thewaste water has a pH outside the range of 5 to 9,purification thereof can be performed to some extent by theelectrolysis; but in this case the efficiency of purification is verysmall.

Further, during the electrolysis, all the polluting substances, such asheavy metallic ions of zinc, copper, lead, cadmium, mercury, etc.besides fats and oils, hydrogen sulfide, and other fine suspendedsolids, all of which have been contained within the waste water from thebeginning, can be removed therefrom.

As the electrolysis proceeds, all these polluting substances arecoagulated together with the floc arising from the ligninsulfonate. Theyare floated by the elecvtrolysis and are concentrated as scum on thesurface of waste water (or purified liquid) is discharged from theoutlet disposed on the side wall or near the bottom of the electrolyticcell.

As above-described, a method according to the pres- The amount ofremoved sodium ligninsulfonaterdiffered in accordance with theconcentration thereof within the waste water. When the waste watercontained less than 1,000 ppm of sodium ligninsulfonate,

ent invention, wherein the electrolysis is conducted by 5 the COD valuewas decreased to 1/10 or so by 1 hour employing a ferrous anode plateand utilizing the waste electrolysis.

water as an electrolyte, does not need any of separation ln addition,the foregoing was also observed, when cells having a complicatedstructure, and feeding dethe aqueous solution contained calcium salt orpotasvices by pressure, etc. that are employed by the consium salt ofligninsulfonic acid.

' TAIKE 1 COD of the limpid liquid staying in the lower Waste waterbefore the start of electrolysis portion of the cell after the start ofelectrolysis (ppm) after the start of electrolysis in minutesConcentration of sodium ligninsulfonate COD (ppm) (ppm) I0 4O 60 90 120240 300 360 500 398 200 113 63 42 27 16 6 8 6 1000 840 800 760 l70 85 6038 l9 17 2000 I524 468 3l2 264 64 53 39 39 5000 3520 3520 3440 2880 960824 792 I90 103 92 ventional methods.

Further, a method according to the present invention can be applied tothe treatment of almost all the waste waters of sulfitepulping,'especially waste water con- DESCRIPTION OF THE PREFERREDEMBODIMENT Each of aqueous solutions containing 500 ppm, 1,000 ppm,2,000 ppm, and 5,000 ppm of sodium ligninsulfonate respectively wastaken individually into a 5-liter cell provided with a ferrous anodeplate. Then, each of aqueous solutions was subjected to electrolysiswith an electric current of 5A and cell voltage of 4.0 V, while air wasblown into the cell by an air pump, so as to separate insolublesubstances from the mother liquid by floating them.

During the electrolysis as above-mentioned, an examination was carriedout, at regular intervals of time, for observing the removal of sodiumligninsulfonate from the mother liquid by checking the COD (ChemicalOxygen Demand) of the liquid by sampling the limpid liquid staying inthe lower portion of the cell. The results are shown in Table l.

What is claimed is:

1. A process for the electrolytic purification of waste water containingligninsulfonate, which comprises: placing said waste water having a pHin the range of from 5 to 9, as an electrolyte, in an electrolytic cellhaving cathode means and iron anode means; electrolyzing said wastewater in said cell and adding acidic substance to the waste water tocontinuously maintain the pH thereof in said range so that said ironanode means dissolves in said waste water and insoluble substances areproduced in said waste water; blowing air into said waste water in saidcell during the electrolysis to oxidize ferrous ions in said waste waterto ferric ions and to remove adhering substances from the surfaces ofsaid cell, the insoluble substances produced in said cell including saidligninsulfonate forming a floc which absorbs said air and the gasgenerated by the electrolysis and floats t0 the upper surface of thewaste water in the electrolytic cell and forms a layer of scum thereon;removing purified waste water from the lower part of the cell; andremoving scum from the upper part of the cell.

2. A process of treating the waste water containing ligninsulfonateaccording to claim 1, wherein said lig-' ninsulfonate is the sodiumsalt, potassium salt, or calcium salt of ligninsulfonic acid.

2. A process of treating the waste water containing ligninsulfonateaccording to claim 1, wherein said ligninsulfonate is the sodium salt,potassium salt, or calcium salt oF ligninsulfonic acid.